Niki's NotesTransport systemsSimple organisms Organisms such as Amoeba can rely on simple diffusion to get all of the substances theyneed. Nutrients and oxygen can diffuse into the cell and waste can diffuse out. This is because theseorganisms have a large surface area to volume ratio. Because the Amoeba is a single cell, there isless distance for substances to travel, and diffusion is much quicker. Remember: the bigger the organism, the smaller the SA : Vol ratio!Large organisms These organisms are made of lots of cells, so substances need to travel long distances fromthe outside to the cytoplasm of all the cells. Simple diffusion would not be suitable for this asnutrients would not be able to reach the cells fast enough. Humans use the heart and circulatorysystem as a mass transport system to do this. Substances are transported through the in the flow ofa fluid with a mechanism for moving it around the body. Processes such as osmosis, diffusion andactive transport are involved as well.Mass transport system: Features A suitable transport medium A system of vessels to carry substances A way of ensuring that substances are moved in the right direction A quick way of moving materials to meet the needs of the organism or a way of maintaining a concentration gradient.

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Niki's NotesWater in living organismsWater has the chemical formula HO. Water molecules are described as slightly polarised becausethey have a slight positive charge at one end of the molecule and a slight negative charge at theother end. As a result, individual molecules form hydrogen bonds with each other.Water is an important solvent in living organisms because most biochemical reactions take place inaqueous solution.…read more

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Niki's Notes The Heart (Cardiac cycle) All arteries (except the pulmonary arteries) take oxygenated blood away from the heart. The valves close up to stop blood from going back into the heart. Mammals have a double circulation consisting of a pulmonary (to lungs) and systemic (to the rest of the body) circulations. Blood is transferred to and from the heart twice.…read more

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Niki's NotesDiastole: 1. The heart is at rest and the myocardium is relaxed. 2. The atria and ventricles passively fill with blood (AV valves) 3. The aortic and pulmonary artery semilunar valves are closed, bi and tri are openAtrial Systole: 1. The atria contract and the ventricles relax 2. Remaining blood is forced into the ventricles 3. The bicuspid and tricuspid are open, semi-lunar valves closedSystole: 1. The atria contract and eject the final amount of blood into the ventricles. 2.…read more

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Niki's NotesSA node ­ pacemaker, because it determines the rate of contraction of the rest of the cardiacmuscle (Where the vena cava enters the right atrium)Intrinsic rhythmicity ­ In early embryo cells that are destined to become the heart, begincontracting long before the heart forms.…read more

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Niki's NotesFactors that affect membrane fluidity 1. Temperature ­ at lower temps, lipids have less kinetic energy so are packed more tightly, decreasing fluidity. High temps = loose lipids, more fluidity. 2. Lipids ­ Long with saturated tails have a high melting point, which decreases fluidity. The straight unkinked fatty acid chains mean the lipid molecules can pack together more tightly. 3. Cholesterol ­ (Normal body temp) Low levels can make the membrane too fluid, and may cause the cell to burst.…read more

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Niki's NotesDiffusion and gas exchangeFacilitated diffusion ­ proteins in the membrane allow only specific substances to move throughpassively down their concentration gradient.OsmosisHypotonic ­ The osmotic concentration of solutes is lower than that in the cytoplasm of the cells.Water enters the cell.Isotonic ­ There is no net gain or loss of water. The solution has the same osmotic concentration asthe cell.Hypertonic ­ The osmotic concentration of solutes is higher than that in the cytoplasm.…read more

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Niki's NotesBloodPlasma - mostly water with dissolved nutrients, salts, hormones and proteins Largely water Contains fibrinogen, a substance vital for blood clotting Contains a range of dissolve substancesPlatelets ­ cell fragments involved in blood clotting Tiny fragments of larger cells called megakaryocytes found in bone marrowWhite Blood cells (leucocytes) ­ help fight infection Much larger than erythrocytes but can change their shape to fit through small blood vessels Between 4000 and 10000 per cubic ml of blood Most are formed I…read more

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Niki's NotesThe vesselsArteries They carry blood away from the heart (except pulmonary artery) Arteries near the heart have the most elastic fibres to withstand high blood pressure Blood pressure in the arteries decreases the further away it is from the heart The diameter of the lumen changes.…read more

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Niki's NotesGas exchange in the alveoliInhalation (active) The muscles around the diaphragm contract and it is lowered and flattened. The intercostals muscles between the ribs also contract, raising the rib cage upwards and outwards. The volume of the chest cavity increases, reducing the pressure in the cavity. This pressure is now lower than the pressure of the atmospheric air outside, so to equalise the pressure, air moves in through the trachea, bronchi and bronchioles into the lungs.…read more